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Abstract

Conductive diamond has exceptional chemical stability, making it an appealing candidate material for long-term medical device implants. This work describes the characterization, and fabrication of four diamond-based neural devices. A previously developed 30 µm diamond-disk in vitro needle electrode was characterized. The device could detect 1 nM concentration analytes in a flow cell using fast scan cyclic voltammetry, but the fabrication was not reproducible. A novel in vitro diamond device was developed with diamond selectively grown at the tip of a hollow quartz capillary, resulting in a 2-4 µm tip diameter. The diamond tip shape and size were geometrically reproducible, although an electrical connection to these tips is still needed. Two novel in vivo diamond based devices were also fabricated. The first generation in vivo diamond electrode was assembled by attaching a brittle diamond electrode to a flexible insulated substrate. The device fabrication time was 6 hrs of hands-on activity, but it was successfully implanted in a freely behaving Aplysia californica. Electrical recordings were compared to a stainless steel standard for two surgeries, respectively 8 days post surgery and 12 days post surgery. However, external electrical connections to equipment had sufficiently large noise and signal variability. No definitive conclusions could be reached about differences in recordings by diamond and steel.A second generation in vivo diamond electrode was fabricated on a substrate that remained flexible after diamond growth, also reducing the fabrication time by 4 hrs. Substrates typically become embrittled during diamond growth because of surface carbide formation. Two rhenium alloys, 75% tungsten / 25% rhenium (v/v) and 47.5% molybdenum / 52.5% rhenium (v/v), were investigated as flexible substrates that might not form carbides during diamond growth but adhere strongly to diamond. Three growth times were explored, with the rhenium alloys compared to a traditional tungsten substrate. Diamond grown for 20 hours on 47.5% molybdenum / 52.5% rhenium alloy had the highest diamond quality (crystal size, sp3 content, and good electrochemical activity), with the substrate remaining flexible after the diamond growth. This device has not yet been insulated with a biocompatible material; however, in vitro recordings were obtained with Aplysia.